1. Field of the Invention
The present invention relates to a projection headlamp of the type in which light beams reflected by a substantially elliptical reflector are projected forward by a projection lens. More particularly, the invention relates to a projection headlamp for automobiles capable of selectively changing a beam distribution pattern from one pattern to another by tilting a shade.
2. Discussion of the Related Art
Conventional headlamps of this type are disclosed in an Unexamined Japanese Utility Model Application (OPI) No. Sho. 63-41801 and Unexamined Japanese Patent Application (OPI) No. Hei. 1-213901. The headlamp of the former Japanese publication is constructed as shown in FIG. 1. As shown, a light source 3 is positioned at the first focal point F1 of a reflector 2 which has a substantially elliptical shape, and a shade 4 is located near the second focal point F2. A projection lens 5 is disposed in front of the shade 4. In the headlamp thus constructed, for selectively changing a beam distribution pattern from one beam pattern to another, for example, a subbeam distribution pattern to a main beam distribution pattern, the shade 4 is rotated about a horizontal support shaft O, to partially intercept light beams directed toward a projection lens 5. In the figure, reference numeral 1 designates a lamp body, and numeral 6, a front lens.
The headlamp of the latter conventional Japanese Patent publication employs shade rotating means (not shown) different from that of the former Japanese Utility Model publication, but the headlamps are both based on the same idea that, to select the main beam distribution pattern or the sub-beam distribution pattern, the shade is rotated.
The conventional headlamps thus constructed is capable of selecting one of merely two patterns, i.e., the main beam distribution pattern and the sub-beam distribution pattern. In other words, it cannot freely select a beam distribution pattern, e.g., a medium beam distribution pattern of a middle state between the main beam and sub-beam distribution patterns.
To cope with this, the present inventors have proposed a technique as disclosed in a co-assigned U.S. patent application Ser. No. 08/070,902 filed on Jun. 3, 1993. In this technique, as apparently illustrated in FIG. 2, a shade a is formed of a rotary tubular body having a step a. The rotational axis c of rotation of the shade a is eccentric with respect to the axis of the shade a. Accordingly, when the shade a is rotated, the clear cut line of the light beam distribution pattern vertically moves between clear cut lines Pa and Pb as shown in FIG. 2. Thus, in the construction of the headlamp of FIG. 2, the clear cut line is movable vertically.
However, it is more preferable that the shade and the step move also horizontally along the axis not only moves vertically, because in driving an automobile with the headlamps of the right-side beam distribution patterns, when a driver turns the automobile to the right, he would have a difficulty to see well the right corner, and vice-versa.